Technical Abstract:
Dispersal and post-dispersal predation of Italian ryegrass seed in unimproved pasture.
Italian ryegrass (Lolium multiflorum L.) can be a productive and high-quality cool-season forage, but is considered a weed in some pastures. Italian ryegrass does not form a persistent seed bank and needs to produce sufficient seed annually for effective re-establishment. Here we examine two factors involved in seed bank development: seed dispersal and post-dispersal predation. For the dispersal study, seed traps (15-cm dia.) were placed at intervals of 0, 0.3, 0.6, 0.9, 1.2 and 1.8 m from the edge 1-m2 uniform, grass blocks in the eight cardinal directions. Trapped seed were counted every 7 to 10 days until the ryegrass was harvested in July. Insect predation of ryegrass seed over a 12-month period was determined from May 2006 to June 2007 with cards baited with 30 ryegrass seed. The cards were collected weekly and replaced with fresh cards. Although some seed (8%) were trapped at 1.8 m, 80% of the seed were found at 1 m or less from the edge of the plot. Mowing increased the seed deposited at the edge of the plot and further seed were deposited along the direction the forage was raked for removal. Weekly mean seed predation ranged from 6 to 86 % over the 12-month period. Mean predation was greater in the winter months (53%) than in the summer (34%) or fall (26%). Predators noticed in the field were mainly harvester ants, but crickets and other predators were observed. These studies indicate that the majority of the Italian ryegrass seed remains in the seed head. The seed that is dispersed falls within the shadow of the parent plant, most within 1-m distance, and the post-dispersal seed predation in our system is approximately 40% over a 12-month period.